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Important Topics: Bhalani II Year Final Exam

1. General Microbiology and Immunity

Immunology (High Priority)

• IgG - structure and function (LAQ)
• IgM - properties, functions, structure (***) - very important
• Immunoglobulins - classify, sub-classes
• IgA - diagram

• Agglutination reactions - types, principle, applications; Widal Test; Tube Agglutination
• Precipitation reactions - principle, applications
• ELISA with applications
• Prozone Phenomenon
• Passive Agglutination tests

• Classify hypersensitivity reactions (Gell & Coombs)
• Type I Hypersensitivity (IgE-mediated / Anaphylaxis) - LAQ (multiple entries)
• Type III Hypersensitivity (Immune complex) - describe
• Type IV Hypersensitivity (Delayed-type / Cell-mediated) - LAQ
• Immediate vs delayed hypersensitivity types with examples

• Classical Pathway of Complement (*)
• Complement cascade and biological effects

• Define, mechanisms of autoimmunity (LAQ)
• Four features of autoimmune diseases

• Innate Immunity - mechanisms
• Cell Mediated Immunity - tests for detection

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General Microbiology

• Bacterial Growth Curve (**)
• Bacterial Spore
• Bacterial Capsule - describe, detection methods
• Cell Wall of Gram Positive Organisms - structure and functions
• Bacterial Flagella

• Autoclave - principle, applications (**); diagram
• Hot Air Oven - role
• Dry Heat sterilization methods
• Moist Heat methods
• Four chemical agents for disinfection; properties of ideal disinfectant

• Mutational and Plasmid-mediated drug resistance (*** - six differences)
• Gene transfer in bacteria: Transduction, Conjugation (LAQ)

• Embryonated Hen's Egg - routes of inoculation, uses (*)
• Methods of detecting viral growth in cell cultures (***)
• Inclusion Bodies (****) - intracytoplasmic and intranuclear examples
• Negri bodies

• Classification of medically important fungi (*)
• Morphological classification with examples (LAQ)

• Biomedical wastes - define, categories, disposal, colour code (*)
• Hospital-Acquired Infections (LAQ)
• Pyrexia of Unknown Origin (PUO) - etiological agents, diagnosis (*)
• Universal Safety Precautions

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2. CVS and Blood (Bloodstream & CVS - Microbiology)

High-Priority Topics

• Salmonella Typhi - Enteric Fever - laboratory diagnosis
• Widal Test - principle, application
• Co-Agglutination Test
• Lab tests to diagnose Enteric Fever in 1st week

• Leptospira - pathogenesis, laboratory diagnosis
• Syphilis - serological diagnosis (VDRL - principle, applications, advantages, limitations)
• Leptospirosis - full workup

• Pathogenesis; window period definition
• Laboratory diagnosis (**) - HIV Testing strategies in India
• Opportunistic infections (two examples)
• Diagram of HIV
• Enumerate organisms causing STDs

• Immunoprophylaxis (**), dosage schedule
• Non-neural vaccines and schedule

• Laboratory diagnosis
• Plasmodium falciparum - complications (*), laboratory diagnosis
• Malignant Tertian Malaria - life cycle, complications, lab diagnosis (LAQ)
• Plasmodium vivax - morphology, life cycle, lab diagnosis (LAQ)

• Leishmania donovani - life cycle, Kala Azar - pathogenicity, lab diagnosis (LAQ) (*)
• LD Bodies
• Wuchereria bancrofti - morphology, lab diagnosis

• Opportunistic mycoses (*) - short note
• Candida albicans (*) - lab diagnosis
• Fungi causing opportunistic infections in HIV - enlist (LAQ)
• Reynolds Braude phenomenon
• Histoplasma Capsulatum - morphology, pathogenesis

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3. Gastrointestinal and Hepatobiliary System (Microbiology)

GIT - Very Frequently Asked

• Clostridium botulinum - pathogenicity, prevention
• Nagler Reaction (**) - principle, procedure, use

• Classical vs El Tor vibrios - differences (**)
• Laboratory diagnosis (*)
• Gardner and Venkataraman's classification
• Halophilic Vibrios (*) - two examples
• Kanagawa Phenomenon (*)
• Pathogenesis (LAQ)

• Types causing diarrhoea (ETEC, EPEC, EHEC, EIEC, EAEC)
• Enterotoxigenic E. Coli
• One lab test to diagnose each type

• Laboratory diagnosis (****)
• Pathogenesis (**)
• Salmonella diseases caused

• Shigella dysentery - pathogenicity, lab diagnosis
• Classify Shigella; mechanism of dysentery production

• Staphylococcal food poisoning
• Organisms responsible, pathogenesis, lab diagnosis

• Ascaris lumbricoides - life cycle (), lab diagnosis (), pathogenicity, complications () (LAQ)
• Hookworm (*) / Ancylostoma duodenale - morphology, life cycle, pathogenesis, lab diagnosis (LAQ)
• Enterobius vermicularis - life cycle, pathogenicity, lab diagnosis (LAQ)
• Strongyloides stercoralis hyperinfection
• Ectopic Ascariasis
• Nematodes - classify

• Taenia saginata vs Taenia solium - four differences (**); Taenia solium tissue cyst (CNS chapter also)

• Acute Giardiasis - lab diagnosis, findings

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Hepatobiliary - Microbiology

• Classify hepatitis viruses; mode of transmission
• Laboratory diagnosis (****) - serology
• Pathogenesis of HBV (*)
• Morphology of HBV
• Enumerate serological markers (HBsAg, HBeAg, Anti-HBc, Anti-HBs etc.)
• Prophylaxis

• Laboratory diagnosis specifically

• Causative agent, sites affected, cross-section structure
• Life cycle (LAQ)

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Star-Rated Priority Summary

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• LAQs to master: Hepatitis (classify + lab diagnosis), Hypersensitivity (Type I, III, IV), Antigen-Antibody reactions (agglutination + precipitation), Vibrio cholerae, Ascaris/Hookworm life cycles, HIV, Sterilization/Autoclave, Autoimmunity
• SNs to cover: Every topic with 2+ stars above
• Topics in the PDF marked with * appeared in previous exams; *** and above = recurring favourites

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EXAM ANSWERS: 6-Star to 2-Star Topics

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⭐⭐⭐⭐⭐⭐ 6-STAR TOPIC

CLOSTRIDIUM (GIT)

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Clostridium botulinum - Pathogenicity and Prevention

Pathogenicity

• Toxin is absorbed from GIT (food-borne) or produced in wound/intestine
• It binds irreversibly to presynaptic terminals at neuromuscular junctions
• Blocks release of Acetylcholine (ACh) → flaccid paralysis
• Toxin has two fragments: Heavy chain (binding) + Light chain (Zn-dependent protease that cleaves SNARE proteins)

1. Food-borne botulism - ingestion of preformed toxin in improperly canned/processed food. Symptoms: nausea, vomiting, diplopia, dysarthria, descending flaccid paralysis, no fever
2. Wound botulism - toxin produced in infected wound
3. Infant botulism - most common form; ingestion of spores (honey) → colonization in infant gut → toxin production
4. Iatrogenic botulism - complication of therapeutic botulinum injections

Prevention

• Proper heat processing of canned foods (boiling destroys toxin; spores need 121°C autoclave)
• Avoid giving honey to infants under 1 year
• Wound care and debridement

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Nagler Reaction

• C. perfringens produces alpha toxin (lecithinase C / phospholipase C)
• This enzyme splits lecithin in egg yolk medium → forms turbid precipitate (opalescence)
• Clostridium perfringens antitoxin (anti-alpha toxin) inhibits this reaction on one half of the plate

1. Egg Yolk Agar (EYA) plate is divided into two halves
2. One half is spread with C. perfringens antitoxin
3. Organism is streaked across both halves
4. After anaerobic incubation at 37°C for 24-48 hours

• Side WITHOUT antitoxin: Turbid/opalescent precipitate (pearly layer) around colonies = Nagler Reaction POSITIVE
• Side WITH antitoxin: No turbidity = inhibited = confirms the reaction is due to alpha toxin

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Gas Gangrene - Pathogenesis and Laboratory Diagnosis

• Alpha toxin (lecithinase): Most important - causes cell membrane lysis, haemolysis, myonecrosis
• Theta toxin: Cardiotoxic, leucotoxic
• Kappa toxin: Collagenase (tissue destruction)
• Mu toxin: Hyaluronidase (spreading factor)
• Nu toxin: DNase

Laboratory Diagnosis

1. Gram stain: Large Gram-positive rods, few/absent WBCs (toxin kills leukocytes), absence of spores in tissue
2. Culture: Anaerobic culture on Blood agar, Robertson's cooked meat medium (RCMB)
   • Blood agar: Double zone of haemolysis (inner complete beta, outer partial alpha)
3. Nagler Reaction: Positive (as described above)
4. Biochemical tests: Stormy fermentation of milk (RCMB with litmus milk)
5. X-ray: Gas in tissues (gas shadows in muscles)

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⭐⭐⭐⭐⭐ 5-STAR TOPIC

HEPATITIS - Classify, Lab Diagnosis, HBV Pathogenesis, Serology

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Classification of Hepatitis Viruses

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Hepatitis B Virus (HBV) - Pathogenesis

• Outer envelope: Contains HBsAg (Hepatitis B surface antigen)
• Inner nucleocapsid: Contains HBcAg (core antigen), HBeAg, circular partial dsDNA + DNA polymerase

1. HBV enters hepatocytes via NTCP receptor (Sodium taurocholate co-transporting polypeptide)
2. Viral DNA enters nucleus → converted to cccDNA (covalently closed circular DNA) - the viral reservoir
3. HBsAg, HBcAg, HBeAg are produced; assembled virions bud from ER
4. Liver damage is IMMUNE-MEDIATED, not directly cytopathic:
   • CD8+ cytotoxic T lymphocytes (CTLs) attack HBcAg-expressing hepatocytes
   • TNF-alpha, IFN-gamma contribute to inflammation
5. Strong immune response → acute hepatitis → clearance
6. Weak/inadequate immune response → chronic hepatitis → cirrhosis → HCC

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Serological Markers of HBV - Sequence in Acute Infection

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Laboratory Diagnosis of Viral Hepatitis

• Anti-HAV IgM - acute infection (gold standard)
• Anti-HAV IgG - past infection / immunity

• HBsAg - current infection (acute or chronic)
• Anti-HBc IgM - acute/recent
• HBeAg - high infectivity
• HBV DNA (PCR) - gold standard for viral load
• Anti-HBs - recovery / vaccination

• Anti-HCV antibody (ELISA/RIBA) - screening
• HCV RNA by RT-PCR - confirmatory; detectable in 1-2 weeks (before antibody)
• HCV genotyping - determines treatment duration

• Anti-HDV IgM/IgG; HDV RNA PCR
• Only occurs with HBV (co-infection or superinfection)

• Anti-HEV IgM - acute
• HEV RNA - in acute illness

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⭐⭐⭐⭐ 4-STAR TOPICS

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VIBRIO CHOLERAE (****)

Gardner and Venkataraman's Classification

• O1 (Epidemic cholera): Classical and El Tor biotypes
• O139 (Bengal strain): Emerged 1992, epidemic in India/Bangladesh
• Non-O1/Non-O139: Cause sporadic gastroenteritis, no epidemics

Classical vs El Tor Biotypes - Differences

Pathogenesis of Cholera

1. Ingestion of contaminated water/food (infective dose: 10^8 organisms)
2. Survives gastric acid → colonizes small intestine (aided by motility, mucinase, haemagglutinin)
3. Produces Cholera Toxin (CT): A-B subunit toxin
   • B subunit (5 copies): binds GM1 ganglioside on enterocyte surface
   • A subunit enters cell → irreversibly activates adenylyl cyclase via ADP-ribosylation of Gs protein
   • Massive increase in cAMP → hyperactivation of Cl- channels (CFTR) → massive Cl- and water secretion
4. Result: Rice-water diarrhoea (10-20 L/day), severe dehydration, hypovolemic shock, metabolic acidosis, hypokalemia

Laboratory Diagnosis of Vibrio cholerae

1. Direct microscopy: Gram stain - comma-shaped Gram-negative rods; Dark field - "shooting stars" motility
2. Culture:
   • Enrichment: Alkaline Peptone Water (APW) pH 8.6 - inhibits other organisms
   • Selective medium: TCBS (Thiosulfate Citrate Bile Salts Sucrose) agar - yellow colonies (sucrose fermenter)
   • Blood agar: Grey, translucent colonies, non-haemolytic (Classical) or beta-haemolytic (El Tor)
3. String test: Positive (colonies become mucoid/stringy when mixed with 0.5% sodium deoxycholate)
4. Oxidase test: Positive
5. Slide agglutination: With polyvalent O1 antiserum
6. Biotyping: Voges-Proskauer test, haemolysis test, polymyxin B sensitivity

Kanagawa Phenomenon

• Beta-haemolysis produced by V. parahaemolyticus on Wagatsuma (blood) agar
• Indicates pathogenic strains (Kanagawa positive = virulent; produces thermostable direct haemolysin - TDH)

Halophilic Vibrios

• Require NaCl (salt) for growth
• Examples: V. parahaemolyticus (seafood poisoning), V. vulnificus (wound infection, septicaemia)

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INCLUSION BODIES (****)

Intranuclear Inclusion Bodies

Intracytoplasmic Inclusion Bodies

• Negri bodies = Rabies (most commonly asked)
• Guarnieri = Smallpox/Vaccinia
• Owl-eye = CMV (can be intra-nuclear AND intracytoplasmic)

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ENTERIC FEVER - Laboratory Diagnosis (****)

Week-by-Week Laboratory Diagnosis

Widal Test

• O antigen (somatic - LPS): IgM antibody - rises early
• H antigen (flagellar): IgG antibody - rises later, persists longer

• Significant titre: O antigen ≥1:80; H antigen ≥1:160 (endemic areas may require higher)
• Rising titre (4-fold increase in 2 samples taken 1 week apart) is more diagnostic
• Limitations: False positive in previous vaccination, cross-reactions with other Salmonella spp., other infections; false negative in early disease, antibiotic treatment

• Uses antibody-coated Staphylococcus aureus (Cowan I strain) to detect Salmonella antigens in serum/urine/CSF
• Used for rapid diagnosis in Week 1 (detects antigen, not antibody)
• More specific than Widal in 1st week

Other Tests

• Bone marrow culture: Most sensitive (90%+), positive even after antibiotics started
• ELISA: Detect Vi antigen (carrier detection) or specific IgM
• PCR: Not routine

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⭐⭐⭐ 3-STAR TOPICS

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SPIROCHETES (***)

Classification of Spirochetes

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Syphilis - Serological Diagnosis

Non-Treponemal Tests (Screening)

• VDRL (Venereal Disease Research Laboratory):
  • Detects reagin (IgG + IgM antibodies against cardiolipin-lecithin-cholesterol antigen)
  • Flocculation test
  • Advantages: Cheap, simple, quantitative (titres correlate with disease activity)
  • Limitations: False positives (SLE, malaria, leprosy, pregnancy, viral infections - "SMILEV"); must confirm with treponemal test
  • Uses: Screening, monitoring treatment response (titres fall with successful treatment)
• RPR (Rapid Plasma Reagin): Similar principle, uses carbon particles, can be read macroscopically

Treponemal Tests (Confirmatory)

• FTA-ABS (Fluorescent Treponemal Antibody Absorption): Most sensitive; first to become positive
• TPHA/TPPA (Treponema pallidum Haemagglutination Assay): Sensitive and specific; easy to perform
• MHA-TP: Microhaemagglutination
• Western Blot: Reference standard

• Primary: Dark-field microscopy of chancre exudate (direct), FTA-ABS (first serological test to turn positive)
• Secondary: All tests positive; VDRL titres highest
• Latent: Only serology (no clinical signs)
• Tertiary: TPHA/FTA-ABS positive; VDRL may be weakly positive or negative

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Leptospirosis - Pathogenesis and Laboratory Diagnosis

1. Entry through skin abrasions or mucous membranes from water/soil contaminated with infected animal urine
2. Leptospiraemic phase (Days 1-7): Fever, headache, myalgia (leptospires in blood, CSF)
3. Immune phase (Week 2+): Antibodies appear, leptospires enter organs
4. Weil's Disease (severe form): Jaundice + renal failure + haemorrhage (LFT: hepatitis pattern; acute tubular necrosis)

• MAT (Microscopic Agglutination Test): Gold standard serology; titre ≥1:100 diagnostic; titre ≥1:400 highly significant
• ELISA: IgM antibody detection (point-of-care tests)
• PCR: Early diagnosis (Week 1)

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ANTIGEN-ANTIBODY REACTIONS (***)

General Features (Laws of Serology)

• Specific (antibody reacts only with homologous antigen)
• Reversible (governed by hydrogen bonds, Van der Waals forces, ionic bonds)
• Involve primary binding (formation of Ag-Ab complex) and secondary phenomena (visible reaction)
• Optimal ratio (zone of equivalence) needed for visible precipitation/agglutination
• Prozone phenomenon: Excess antibody → no visible reaction (all antigen binding sites occupied)

Agglutination Reactions

1. Direct/Active Agglutination: Antigen is naturally present on particle (RBCs, bacteria)
   • Widal test (bacterial agglutination for Salmonella)
   • Blood grouping (ABO/Rh)
2. Passive/Indirect Agglutination: Soluble antigen coated on carrier particles
   • TPHA (Treponema antigen coated on RBCs)
   • Latex agglutination tests (RA factor, CRP, cryptococcal antigen)
3. Reverse Passive Agglutination: Antibody coated on particles to detect antigen
4. Haemagglutination Inhibition (HI): Virus is added; if specific antibody present, it inhibits haemagglutination (influenza diagnosis)

• Serial dilutions of patient serum + standardised antigen suspension
• Incubate → read agglutination
• Highest dilution showing agglutination = titre

• Excess antibody in lower dilutions paradoxically gives negative result
• Solution: Dilute serum further before testing

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Precipitation Reactions

1. Ring/Interface precipitin test (Ascoli's test): Antigen layered over antibody in tube; precipitate at interface
2. Slide/Tube precipitation (VDRL)
3. Double Immunodiffusion (Ouchterlony): Antigen and antibody diffuse toward each other in gel; precipitin line forms at equivalence zone
4. Single Immunodiffusion (Radial Immunodiffusion - RID/Mancini): Antigen diffuses into antibody-containing gel; circular precipitin ring
5. Immunoelectrophoresis (IEP): Electrophoresis + diffusion against antiserum
6. Counter-current Immunoelectrophoresis (CIEP): Rapid precipitation using electric current

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HYPERSENSITIVITY (***)

Gell and Coombs Classification

Type I Hypersensitivity - Detail

1. First antigen exposure → APC presents to Th2 cells
2. Th2 releases IL-4, IL-13 → B cells class-switch to produce IgE
3. IgE binds to FcεRI receptors on mast cells and basophils (sensitization; no symptoms)

1. Antigen cross-links IgE on mast cells
2. Degranulation releases:
   • Preformed: Histamine, tryptase, heparin
   • Newly formed: Leukotrienes C4/D4/E4 (bronchoconstriction), PGD2, PAF
3. Early phase (minutes): Vasodilation, smooth muscle contraction, increased vascular permeability
4. Late phase (hours): Eosinophil/neutrophil infiltration (leukotrienes, cytokines)

• Systemic anaphylaxis: Hypotension, bronchospasm, angioedema (bee sting, penicillin, peanuts); treat with adrenaline
• Bronchial asthma: Allergen triggers bronchoconstriction
• Hay fever (allergic rhinitis): Seasonal; grass pollen
• Urticaria and atopic dermatitis

Type IV Hypersensitivity - Detail

1. Antigen processed by APCs → presented to CD4+ Th1 cells via MHC II
2. Th1 cells release IFN-gamma → macrophage activation → granuloma formation
3. CD8+ CTL cells mediate direct cytotoxicity

• Tuberculin test (Mantoux): Intradermal PPD injection → indurated erythema 48-72 hrs
• Contact dermatitis: Nickel, rubber, poison ivy
• Granulomatous hypersensitivity: Tuberculosis, leprosy, schistosomiasis
• Graft rejection (cell-mediated)

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MALARIA - Laboratory Diagnosis (***)

Plasmodium Species Causing Human Malaria

Laboratory Diagnosis

• Thick smear: For detecting parasites (more RBCs concentrated → better sensitivity); stained with Leishman or Giemsa
• Thin smear: For species identification (parasite morphology preserved)
• Stain: Leishman stain (used in India) or Giemsa stain

• Multiple ring forms per RBC (>1)
• "Applique" (accole) forms at periphery of RBC
• No enlarged RBCs, no Schuffner's dots
• "Banana-shaped" gametocytes (diagnostic)
• Maurer's clefts in RBC cytoplasm

• Detect HRP2 antigen (P. falciparum specific) or LDH antigen (pan-specific)
• Quick, no microscope needed
• Limitation: Cannot quantify, false negatives in low parasitaemia

• Blood centrifuged in capillary tube with acridine orange dye
• Parasites fluoresce; fast but needs fluorescence microscope

• Most sensitive and specific; used for species confirmation, drug resistance testing, low-level parasitaemia

• Not useful for acute diagnosis; useful for seroepidemiological surveys

P. falciparum - Complications

1. Cerebral malaria: Cerebral sequestration → coma, seizures
2. Severe anaemia: Haemolysis + dyserythropoiesis
3. Blackwater fever: Massive haemolysis → haemoglobinuria (black urine)
4. Acute Renal Failure (ARF)
5. Pulmonary oedema / ARDS
6. Hypoglycaemia
7. Hypersplenism
8. DIC (Disseminated Intravascular Coagulation)

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⭐⭐ 2-STAR TOPICS

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HIV (**) - Pathogenesis, Window Period, Laboratory Diagnosis

Structure of HIV

• Family: Retroviridae; Genus: Lentivirus
• Spherical, ~120 nm; enveloped
• Genome: Two copies of +ssRNA (diploid)
• Envelope: Glycoproteins gp120 (binds CD4) + gp41 (fusion)
• Core: p24 (capsid antigen - most abundant core protein), p17 (matrix), reverse transcriptase, integrase, protease
• Regulatory genes: tat, rev, nef, vif, vpr, vpu

Pathogenesis of HIV Infection

1. Entry: gp120 binds CD4 receptor on T-helper cells (also macrophages, dendritic cells) + co-receptor (CCR5 for macrophage-tropic M-tropic; CXCR4 for T-tropic strains)
2. Fusion: gp41 mediates membrane fusion
3. Reverse transcription: RNA → dsDNA by reverse transcriptase
4. Integration: Viral dsDNA integrated into host chromosomes as provirus (by integrase)
5. Replication: Host cell machinery transcribes provirus → viral proteins → new virions
6. CD4+ T-cell depletion:
   • Direct killing by virus
   • CTL killing of infected cells
   • Bystander apoptosis
   • Syncytia formation
7. Immunodeficiency: CD4 count falls progressively; <200 cells/μL → AIDS (normal: 500-1500)
8. Opportunistic infections emerge as immune system fails

Window Period

• Duration: 2-8 weeks with 4th generation tests (antigen/antibody combo); up to 12 weeks with older antibody-only tests
• During window period: HIV RNA (PCR) and p24 antigen are DETECTABLE
• Importance: Blood transfusion risk; false-negative screening test

Laboratory Diagnosis of HIV

1. ELISA (Enzyme Linked Immunosorbent Assay):
   • 4th generation: Detects both p24 antigen AND anti-HIV antibody
   • Screening test; high sensitivity
2. Western Blot: Confirmatory test; positive if bands for 2 of: p24, gp41, gp120/160
3. HIV RNA PCR: Detects viral RNA in window period; viral load monitoring
4. CD4+ T-cell count: Staging and treatment monitoring (not diagnostic)
5. Rapid tests: ICTC screening; whole blood, results in 30 minutes

• CD4 <500: Oral candidiasis, herpes zoster
• CD4 <200: PCP (Pneumocystis jirovecii pneumonia), Toxoplasmosis
• CD4 <100: CMV retinitis, Cryptococcal meningitis, MAC (Mycobacterium avium complex)
• CD4 <50: CMV disease, disseminated MAC

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IgM (**) - Structure, Properties, Functions

Structure

• Pentameric (5 IgG-like monomers joined by J chain and disulfide bonds)
• MW: ~900,000 Da (largest immunoglobulin)
• 10 antigen-binding sites (valence = 10, but functional valence = 5 due to steric hindrance)
• Contains J chain linking the 5 monomers

Properties

• Normal serum level: 0.5-2 g/L
• Half-life: ~5-10 days
• Does NOT cross the placenta (too large)
• Restricted to intravascular compartment
• First antibody produced in primary immune response
• IgM detected in fetus/neonate = congenital infection (TORCH)

Functions

1. First antibody in primary immune response (later replaced by IgG = class switching)
2. Most efficient complement activator (classical pathway) - single IgM molecule can activate complement
3. Natural antibodies: ABO blood group antibodies (isohemagglutinins) are IgM
4. Agglutination: 750x more efficient than IgG due to pentameric structure
5. Opsonization (less than IgG)
6. Expressed on surface of naive B cells as B-cell receptor (BCR)

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AGGLUTINATION REACTIONS (**) - Summary Table

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STERILIZATION / AUTOCLAVE (**) - Key Points

Definitions

• Sterilization: Complete destruction of ALL microorganisms including spores
• Disinfection: Destruction of vegetative organisms (not necessarily spores)
• Antiseptic: Chemical applied to living tissue to inhibit microorganisms
• Asepsis: Absence of infection / prevention of contamination

Methods of Sterilization

1. Moist Heat (Autoclave) - most reliable
2. Dry Heat (Hot Air Oven)
3. Radiation (UV, gamma)
4. Filtration (Seitz, membrane)

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Autoclave (Steam Under Pressure)

• Temperature: 121°C at 15 lb/inch² (psi) pressure for 15 minutes
• Higher temperature: 134°C at 30 psi for 3 minutes (flash autoclave)

1. Gravity displacement autoclave: Steam enters, displaces cold air downward
2. Pre-vacuum (porous load) autoclave: Air removed by vacuum pump before steam entry
3. Flash autoclave: Rapid; 134°C for 3-5 minutes

• Biological indicator: Bacillus stearothermophilus (Geobacillus stearothermophilus) - spores; most sensitive
• Chemical indicator: Browne's tubes (green → red); autoclave tape (stripes appear)
• Bowie-Dick test: For pre-vacuum autoclaves; checks adequate air removal

• Lower temperature (121 vs 160°C), shorter time, penetrates porous materials, less damage to heat-sensitive items (relative), more reliable

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DRUG RESISTANCE - Mutational vs Plasmid-Mediated (**)

1. Drug inactivation (beta-lactamase hydrolysis of penicillin)
2. Target site modification (PBP2a in MRSA)
3. Reduced permeability (porin changes)
4. Efflux pumps (active extrusion of drug)
5. Bypass of inhibited pathway (sulfonamide resistance - use exogenous folate)

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ASCARIS LUMBRICOIDES (**) - Life Cycle and Laboratory Diagnosis

Life Cycle

1. Ingestion of embryonated egg
2. Egg hatches in small intestine → L2 larva emerges
3. Larva penetrates intestinal wall → enters portal circulation
4. Carried to liver (4-5 days)
5. Migrates to right heart → lungs (5-10 days)
6. In lungs: L2 → L3 → L4 larva; causes Loeffler's syndrome (transient eosinophilia + pulmonary infiltrates)
7. Larvae break into alveoli → ascend via trachea → swallowed
8. Return to small intestine → L4 → L5 (adult worms) in ~10-12 weeks
9. Adults: Female 20-35 cm; Male 15-30 cm; Female lays ~200,000 eggs/day
10. Eggs passed in feces; embryonate in soil in 2-4 weeks

Pathogenicity

• Loeffler's syndrome: Eosinophilic pneumonitis during larval migration
• Intestinal obstruction: Heavy worm load (especially in children)
• Biliary obstruction: Worms enter bile duct
• Ectopic ascariasis: Worms enter appendix (appendicitis), bile duct (jaundice, cholangitis), pancreatic duct
• Nutritional deficiency: Compete for nutrients

Laboratory Diagnosis

1. Stool examination:
   • Direct smear with saline/iodine
   • Concentration methods (Formol-ether sedimentation)
   • Fertilized eggs: Oval/round, bile-stained, thick mammillated coat (outer albuminous coat), 60 x 45 μm
   • Unfertilized eggs: Longer, irregular, thin shell
2. Scotch tape test: For perianal eggs (not Ascaris specifically; used for Enterobius)
3. Serology: ELISA for anti-Ascaris antibodies (epidemiological surveys)
4. Imaging: USG for biliary/intestinal Ascaris; X-ray for intestinal obstruction (worm mass)
5. Worm identification: Adult worm passed spontaneously or post-treatment

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QUICK REVISION TABLE - All Star-Rated Topics